(a) Technical Field
The present invention relates to a display device, and particularly to a display device and a driving method thereof.
(b) Discussion of the Related Art
Generally, a liquid crystal display (LCD) includes a liquid crystal panel assembly. The panel assembly has a plurality of pixels and each pixel includes a switching element and display signal lines. The panel assembly also includes a gray voltage generator generating a reference gray voltage and a data driver generating a plurality of gray voltages. The plurality of gray voltages are generated using the reference gray voltage. A gray voltage corresponding to the image signal among the generated gray voltages is applied as a data signal to the data line among the display signal lines.
The liquid crystal panel assembly includes a display panel provided with the pixel electrode and a liquid crystal layer having dielectric anisotropy. The pixel electrodes are arranged in a matrix and are connected to switching elements such as a thin film transistor (TFT). The switching elements thereby sequentially receive the data voltages row-by-row. The liquid crystal layer on the pixel electrode acts as a liquid crystal capacitor and the liquid crystal capacitor forms a pixel along with a switching element connected thereto.
In the liquid crystal display, the voltage is applied to the pixel electrode to generate an electric field in the liquid crystal layer and the transmittance of light passing through the liquid crystal layer is controlled by controlling the intensity of the electric field, thereby displaying desired images. To prevent a degradation phenomenon or flickering generated as the electric field is applied in one direction for a long period of time, the polarity of data voltages with respect to a common voltage is inverted by frame, row, or pixel.
The gray voltage generator generates reference gray voltages of a predetermined number according to a gamma curve of the liquid crystal display and a group having a positive value and a group having a negative value with respect to the common voltage Vcom are generated. The data driver divides the reference gray voltages to generate gray voltage for all grays and selects the data signal.
When the common voltage Vcom is shifted, the desired luminance might not be obtained, and particularly, display deterioration may be easily recognized in a low gray. Accordingly, the value of the reference gray voltage for the lowest gray is determined to have a predetermined difference from the common voltage Vcom. Accordingly, the available range of the voltage used by the data driver has a predetermined difference from the common voltage Vcom.
In this case, when it is necessary to insert a black image between frames displaying the images, the data driver cannot output the common voltage Vcom such that the complete black may not be realized and the afterimages of the previous frame may remain due to the response speed of the liquid crystal.